In general, torsional dampers relieve a torsional load applied to a crankshaft due to a combustion pressure generated during explosions in each cylinder of an engine. Therefore, the torsional dampers prevent the torsional displacement of the crankshaft from being increased, and thus decrease a risk that the crankshaft is damaged due to fatigue.
As an example of these torsional dampers, a viscous damper applied to a crankshaft of a commercial engine requires high damping performance due to characteristics of the engine. To this end, it is necessary to improve the torsional damping performance of the viscous damper by increasing the inertia mass and size thereof.
For example, the viscous damper includes a case and a cover functioning as a housing accommodating all components, an inertia ring functioning as a medium for converting vibrational energy into thermal energy, silicon oil with which an inner gap is filled by 80% of the whole volume to have an empty volume, the silicon oil serving to absorb thermal energy and emit it to the outside, and a bearing for smoothly maintaining the motion of inertia mass relative to the case. Accordingly, the damping performance of the viscous damper may be easily improved by increasing the inertia mass and inner and outer diameters of the inertia ring.
However, in order to increase the inertia mass and inner and outer diameters of the viscous damper, it is necessary to first resolve the interference with surrounding components in front of the engine due to the layout of an engine compartment.
Thus, the thermal emissivity of the viscous damper is increased by increasing a heat radiation area, thereby allowing the damping performance of the viscous damper to be improved. However, this method has a little effect on an improvement in damping performance compared to the method of increasing the inertia mass and inner and outer diameters of the viscous damper, and the viscous damper is costly to manufacture due to a change in structure or shape of the cover or case.